Paper towel



Patented Oct. 26, 1937 UNITED STATES PATVENTM'OFFI-CE mr s zvm George A.mentaland Milton 0. some, Berlin, N. 11., assignors to Brown Company,Berlin, N. 1-1., a corporation of Maine No Drawing. Application December12,. 1931,

, Serial No. 580,734

'4 Claims. (01. 92-68) Among the important characteristics desired in apaper towel, may be mentioned absorbency, high wetas well as drystrength, softness, absence of removable fuzz or lint, and freedom fromun 5 pleasant odors. In other words, a paper towel should be of suchcharacter that it will rapidly absorb moisture from the skin of theuser, without leaving upon the skin a fuzz of short fiber, and will becapable of being rubbed and manipu- 0 lated during the drying of theskin without tearing, as well as being withdrawn from towel cabinetswithout tearing even when the hands of the prospective userare wet.These desiderata are realized only to a limited extent by theusualwaterleaf paper towels now on the market, made up from the variouskinds of wood pulp, including ground-wood pulp and chemical wood-pulp,such as kraft and sulphite. The fault with these customary towels ofcommerce lies in the fact that in attaining such qualities as softnessand absorbency, substantially unbeaten pulp is used as a raw material,which pulp leads to a paper having comparatively poor strength,especially wet strength, and tear resistance, although having a 25relatively highdegree of absorbency.

In accordance with the present invention, we produce a paper towelwhich, like the towels heretofore made, is substantially free fromnon-cellulosie sizing material but which contains sufilcient cellulosehydrate or gelatinizedmellulose to impart thereto a wet strength vastlygreater than that of a similar waterleaf towel. At the same time, wepreserve the water-holding capacity of our towel at a value not muchless than that of a similar waterleaf towel. In speaking of a "waterleaftowel, we mean a paper towel as heretofore produced,- namely, onelacking not only non-cellulosic sizing materiahbut also any noteworthy,

amount of cellulose hydrate. In speaking of= cellulose hydrate, we meanscellulose fibers which have been hydrated by prolonged beating, whichisa mechanical operation, and/or by the employment of a suitablechemical which can be removed by washing so as to leave with the .fibersno chem- 45 ical which would'have a deleterious effect onthe skin of thetowel user. The expression cellulose hydrate, as we use it in thespecification and in the claims, is not intended to embrace so-calledregenerated cellulose, that is, cellulose which is 50 derived from acellulose derivative of the character of the xanthate, nitrate, or thelike. We have found that we are able to secure the best qualities ofsoftness, absorbency, and high wet and dry strengths by introducing as amore or less 55 continuous phase into a waterleaf paper web sufficientcellulose hydrate or gelatinizedcellulose to increase its wet strengthmarkedly, and then mechanically breaking up the phase to enhance thesoftness and absorbency of the web 50 while still maintaining its wetstrength considerably in excess of the wet strength of a similarwaterleaf web. By carrying out a suitable mechanical manipulation on theweb, the hardened cellulose hydrate can be broken up, not only on thesurfaces of the web, but throughout the web, and be absorbed thereby.Themechanical, manipulation may be effected in a variety of ,ways, as bydrawing 'the web at an acuteangle over a. knife edge or in a tortuouspath past a' series of knife edges in tight frictional contact with theweb. Or the web may undergo the disrupting action of a sand-roll or asand-blast, or be subjected to a suitable creping or crimping operation.7 Rather than using a single lot of pulp 'as the raw material andbeating it 'to generate the appropriate amount of mechanically hydratedcellulose therein, it is possible, and indeed preferable,

to use a batch of pulp in substantially unbeaten" condition and to blendtherewith in suitable amount another batch of thoroughly hydrated orgelatinized pulp, such as serves in the manufacture of so-calledglassine papers. The latter procedurehas the advantage that the batch ofsubstantially unbeaten pulp being made up of fiber units of practicallyoriginal length conduces to a towel web of improved physicalcharacteristics, especially improved tear'resistance. The

g figg Wet tensile pulp in strength of mixture sheets It is to beobserved that the gelatinized pulp markedly increased the wet strengthof the sheets, and that a mixture containing 50% gelatinized pulpyielded a sheet having a wetstrength almost twice as great as thatprepared from a pulp composed entirely of substantially unhydratedfibers. While the sheets containing the gelatinized cellulose were lessabsorbent than the sheet lacking this material, nevertheless a sheetcontaining even as much as 50% gelatinized cellulose can well take up200% by weight of water and can be subjected to creping or othermechanical manipulation designed to enhance its water absorbencymaterially. Such mechanical manipulation can be carried out toappreciate water absorbency greatly, while still maintaining the wetstrength of the sheet considerably above that of a sheet composedentirely of substantially unhydrated pulp.

In making a toweling web containing chemically hydrated cellulose, evenbetter results can be had than through the use of mechanically hydratedcellulose. Thus, we can start with a prefabricated, waterleaf web ofpaper composed entirely of substantially unbeaten pulp, that is, theordinary paper toweling, pass the web through a bath of chemicalhydrating agent under conditions designed to produce the proper amountof cellulose hydrate, then wash the web free of chemical hydratingagent, and-finally dry it. Be-

fore or after drying, the web may be creped or otherwise mechanicallytreated to increase its softness and absorbency. Specifically, thewaterleaf web can beimmersed for a few seconds in nitric acid of 1.42specific gravity at room temperature, then washed free of acid, anddried. We have found that the finished web not only has a wet strengthmany times that of the starting web, but that the increase in wetstrength has been brought about with but little loss in water-holdingcapacity of the web, that is, while keeping its water-holding capacitysubstantially unimpaired, as hereinafter stated. Similar results may beobtained by treating the starting web with dilute formaldehydesolutions, then immersing the web in 72% sulphuric acid at roomtemperature, washing, and drying.-- Qther hydrating agents, like zincchloride and potassium thiocyanate, may be used in such a way as tohydrate or gelatinize the web just far enough to impart the desired wetstrength thereto while keeping its water-holding capacity substantiallyunimpaired.

What we claim is:

1. A process which comprises treating an ab- I then treating the webwith a strong solution of mineral acid at room temperature for a periodof time controlled to permit such acid to hydrate the cellulose andthereby increase markedly the wetstrength of the web while itswater-holding capacity is preserved substantially unimpaired, washingthe web, and subjecting the washed web to a creping operation.

3. A process which comprises treating an absorptive paper web consistingsubstantially entirely of cellulose with dilute formaldehyde solution,then immersing the web in sulphuric acid solution of a strength in theorder of magnitude of about 72% for a period of time controlled topermit such acid to hydrate the cellulose and thereby increase markedlythe wet-strength of the web while its water-holding capacity ispreserved substantially unimpaired, washing the web, and drying it.

4. A process which comprises treating an absorptive paper web consistingsubstantially entirely of cellulose with dilute formaldehyde solution,then immersing. the web in sulphuric acid solution of a strength in theorder of magnitude of about 72% and at room temperature for a period oftime controlled to permit such acid to hydrate the cellulose and therebyincrease markedly the wet-strength of the web whileits water-holdingcapacity is preserved substantially unimpaired, washing the web, andsubjecting the washed web to a creping operation.

- GEORGE A. RICHTER.

MILTON 0. ScHUR;

